A typical present day household refrigerator includes a refrigeration system which circulates refrigerant continuously through a closed circuit including a compressor, a condenser, an expansion device (normally in the form of a capillary tube), and an evaporator back to the compressor. The refrigerant is a two-phase material having a liquid phase and a vapor phase. The refrigeration system operates to cause the refrigerant to repeatedly change from a liquid to a vapor and back to a liquid to transfer energy from inside the refrigerator by removing heat from the refrigerated compartments and expelling it to the atmosphere outside the refrigerator. In a typical refrigerator the evaporator is mounted in the freezer and a fan blows air across the evaporator with the air stream being split so that most of it circulates within the freezer while a portion of it is diverted to circulate through the fresh food compartment. In this way the freezer typically is maintained between about -10.degree. F. and +15.degree. F. while the fresh food compartment is maintained between about +33.degree. F. and +47.degree. F. Such refrigerators do not operate at maximum possible efficiency as the refrigeration cycle produces the refrigeration effect at a temperature which is appropriate for the freezer, but is lower than is required to maintain the fresh food compartment at its appropriate temperature. The mechanical energy required to produce cooling at lower temperatures is greater than that required to produce cooling at higher temperatures and thus the typical simple vapor compression cycle uses more mechanical energy than one which would produce cooling at each of the two desired temperature levels.
Each of U.S. Pat. Nos. 4,910,972 and 4,918,942 discloses a refrigeration system in which a separate evaporator is used to provide the refrigeration for each of the freezer and fresh food compartments. The compressor or compression means in each of these patents takes the form of a two-stage compressor or dual compressors. Refrigerant from the freezer evaporator is fed to a low pressure stage which elevates its pressure to an intermediate level. The vapor stage refrigerant from the fresh food compartment is combined with the refrigerant exiting the low pressure compression stage and all this recirculated refrigerant is then fed to a high pressure compression stage, which raises the refrigerant pressure to the desired relatively high compressor outlet pressure.
Co-pending U.S. patent application Ser. No. 07/612,290 also discloses refrigeration circuits utilizing separate evaporators for the freezer compartment and the fresh food compartment. More particularly, it discloses the use of a compression means combining a single stage compressor with a valve which selectively connects the outlet of the freezer evaporator and vapor stage refrigerant from the fresh food compartment evaporator alternately to the single compressor. Thus, when the valve feeds refrigerant from the freezer evaporator to the compressor, the compressor raises the refrigerant pressure all the way from the low pressure of the evaporator freezer to the desired high compressor outlet pressure. On the other hand, when the valve feeds vapor refrigerant from the fresh food evaporator to the compressor, the compressor only has to raise the pressure from an intermediate pressure level to the desired compressor outlet pressure.
Each of the above-described related patents and application connect the fresh food evaporator and the freezer evaporator in series relationship in the refrigerant flow circuit, with a phase separator connected between them. The phase separator functions to separate vapor stage refrigerant and liquid stage refrigerant with the liquid refrigerant being fed to the freezer evaporator and the vapor refrigerant being fed to the compressor means. In each of these refrigerant circuits the fresh food evaporator is connected in line upstream of the phase separator. With such an arrangement, it is possible that, when the fresh food compartment needs substantial cooling, the fresh food evaporator will cause at least the vast majority of the refrigerant to vaporize. Thus, there may be insufficient liquid refrigerant in the phase separator to appropriately feed the freezer evaporator, resulting in that evaporator being "starved" and the freezer receiving insufficient cooling.
It is an object of the present invention to provide a refrigerator including an improved refrigerant system.
It is another object of the present invention to provide a household refrigerator with separate evaporators for the fresh food compartment and the freezer compartment in which the flow of refrigerant through the fresh food evaporator does not starve the freezer evaporator of refrigerant.
It is another object of the present invention to provide a household refrigerator in which the fresh food evaporator receives refrigerant from a phase separator and returns refrigerant to the phase separator.